This invention relates to telescopic spectacles in general and more particularly to a trial frame for enabling a practitioner to specify a proper frame and prescription to a person having reduced vision.
Telescopic spectacles are widely employed to assist persons who have severe vision handicaps. Essentially, such persons are designated as low vision individuals where, due to deterioration, their vision is reduced by factors of up to ninety percent or more. There are many conditions which will provide such optical atrophy, such as retinal degeneration, partial cataracts and other severe problems. Essentially, the reduction of vision requires such individuals to use spectacles which possess a prescribed carrier lens to enable them to maintain a complete field of vision for use in negotiating in close quarters such as walking up or down steps and for short distance vision and so on.
In regard to such individuals, the carrier lens or spectacles also have coupled thereto a telescopic lens assembly to afford vision at a reduced field of view which will enable such persons to see at longer distances necessary for operating a vehicle, reading, working and so on. Telescopic spectacles are magnifying systems used by persons having such reduced vision.
As indicated, low vision patients have a decreased central vision. Such patients use an area of the retina other than the center or the macula to enable them to utilize their best vision capabilities. Hence, in such individuals, their line of sight which is the line joining the best area of their retina drawn to the point of fixation, is at a different lateral position than the normal line of sight. In order for a practitioner to fit or adjust such an individual with proper telescopic spectacles, the practitioner must be able to accurately measure the line of sight for each patient.
Regular trial frames which are used in normal refraction techniques are not adequate to accommodate low vision patients who require telescopic spectacles. In order to obtain an appropriate fitting in a low vision examination, it is necessary to align the axis of the telescope with the line of fixation of the eye under examination. In order to do so, the practitioner must obtain the exact interpupillary distance between the patient's eyes. In a low vision case, the interpupillary distance of each optic axis of the telescope from the center of the noise piece must be independently located by the practitioner. Apart from this important consideration is that the final spectacle frame to be prescribed for the patient must rest on the nose and ears of the patient in a predetermined orientation. This depends on the width of the bridge, the size of the eye, the length of the temple and the inclination between the temple and the front plane of the spectacle.
In order to properly prescribe a final pair of spectacles for the patient, the practitioner must adjust the patient's vision according to the precise frame or a substantial duplicate of the precise frame that the patient is going to use. For example, typical frame sizes which can accommodate telescopic lenses are available in 44, 46, 48 mm eye sizes and 20, 22, 24 mm bridge sizes with temple lengths of 51/2, 53/4 and 6" in length.
It is an object of the present invention to provide a trial frame which a practitioner can use to specify the optimum position for a telescopic lens assembly employed in spectacles. It is a further object of this invention to provide a trial frame assembly which enables the practitioner to obtain the exact interpupillary distance and to further enable the practitioner to accurately specify the angle of inclination of the telescope about a horizontal axis to thereby enable the patient to achieve the optimum use of the telescope assembly together with correction lenses.